In many instances the characteristics of a particular naturally occurring organic material, such as agricultural, animal and seafood based products can be altered by the removal of certain components soluble in organic solvents. Non-limiting examples of such components include: phospholipids, fish oils, plant oils, fats, fatty acids, alcohols, cholesterol, waxes, gums, stearoids, oil soluble proteins, flavonol, essential oils, natural dyes, and PCBs.
More particularly, oils derived from plant materials, such as oil-seeds, cereal brans, fruits, beans, and nuts, as well as fish oils, are the source of raw material for many important commercial products. For example, oils from plant materials are extensively used in cooking, in cosmetics, pharmaceuticals, as carriers for insecticides and fungicides, in lubricants, in drilling muds, and in myriad other useful products. Consequently, much work has been done over the years in developing improved processes for extracting oil from such materials.
One of the most widely used processes for removing oil from oil-bearing naturally occurring organic materials is solvent extraction. In solvent extraction, the oil-bearing material is treated with a suitable solvent, usually the lower carbon alkanes, at elevated temperatures and pressures, to extract the oil from the oil-bearing material. The resulting solvent/oil mixture is then frationated to separate the valuable oil from the solvent, which is recycled. Most solvent extraction processes in commercial use today employ hexane or carbon dioxide as the solvent. While hexane extraction is the most widely used today, there are also teachings in the art in which normally gaseous solvents are used at both supercritical and subcritical conditions.
One such teaching is found in U.S. Pat. No. 1,802,533 to Reid, wherein a normally gaseous solvent, preferably butane or isobutane, is liquefied by decreasing the temperature and/or increasing the pressure, then passing the solvent through a bed of the oil-bearing material in an extraction vessel. The solvent and extracted oil are then passed to a still where the solvent is separated from the oil. The extracted material must then be placed in another still where it is heated to remove solvent which remained entrained in the extracted material. There is no suggestion of obtaining a substantially solvent-free, dry, extracted material without an additional treatment step after extraction.
Another extraction process is taught in U.S. Pat. No. 2,548,434 to Leaders wherein an oil-bearing material is introduced into the top of an extraction tower and passed counter-current to a liquefied normally gaseous solvent, such as propane, which is introduced at the bottom of the extraction tower. The tower is operated near critical conditions so that the solvent selectively rejects undesired color bodies, phosphatides, gums, etc. The resulting solvent/oil mixture can then be flashed to separate the solvent from the oil. In another embodiment, the solvent/oil mixture is first subjected to a liquid/liquid separation resulting in one fraction containing solvent and a less saturated fatty material, and another fraction containing solvent and a more saturated fatty material. The solvent is then flashed from both fractions. The extracted material remaining in the tower is drawn off and subjected to a vacuum flashing operation to remove entrained solvent.
Also, U.S. Pat. No. 4,331,695 to Zosel teaches a process for extracting fats and oils from oil-bearing animal and vegetable materials. The material is contacted with a solvent, such as propane, in the liquid phase and at a temperature below the critical temperature of the solvent to extract fat or oil from the material. The resulting solvent/oil mixture is treated to precipitate the extracted fat or oil from the solvent by heating the solvent to above the critical temperature of the solvent without taking up heat of vaporization. The extracted residue (shreds) is then treated to remove any entrained solvent, either by blowing it directly with steam, or by indirect heating followed by direct steaming.
In U.S. Pat. No. 5,041,245 to Benado, a continuous solvent extraction method utilizing propane is disclosed to remove oils from vegetable matter, particularly rice bran. According to this method, a sufficient amount of liquid sealing medium is first injected into the vegetable matter in a feeding zone to form a dough-like plastic mass which is compacted and transported by a conveyor assembly to an extraction zone to form a bed. Propane is then introduced into the bed of the extraction zone being operated at 102.degree.-122.degree. F. and 125-250 psig to react with the bed of material. The micella of extracted oil and solvent resulting from this from the reaction of propane and bed material is then separated from the remaining solid residue of the bed material. The propane is then separated from the extracted oil by evaporation or volatilization methods. The preferred separation method is to first subject the micella near its critical pressure (600 psig for propane/rice bran oil mixture) and significantly elevated temperature (190-200.degree. F. for propane/rice bran oil mixture) which can also be near critical. This yields a high solvent light phase (98% solvent, 2% bran oil) and an oil-enriched heavy phase (60% solvent, 40% bran oil). The enriched heavy phase under reduced pressure is then delivered to a heater-evaporator and further treated to form a more oil-enriched heavy phase (10% solvent, 90% bran oil). This phase is then de-pressurized to about one atmosphere, and further treated in a second combined heater-evaporator stage to produce an oil stream having not more than 1-2% propane. Further, similar treatment of this oil stream could be accomplished to remove additional propane if desired.
Other references which teach solvent extraction of oil-bearing materials, with normally gaseous solvents, include U.S. Pat. No. 2,682,551 to Miller, and U.S. Pat. No. 2,560,935 to Dickinson. In each of these processes, the extracted material must be further processed to remove entrained solvent.
Furthermore, there is a great demand for reduced fat prepared food products, especially vegetable and animal-derived fried food products, such as potato chips, fried fast food products, and cheeses. Consequently, the food industry is spending substantial sums of money to bring such products to market. One challenge, particularly for fast food producers is to make a product which is substantially reduced in fat content, but which is still appealing to consumers' taste buds. All too often, these two competing interests are mutually exclusive. There are no commercial processes available wherein vegetable and animal-based food products are first fried, then treated to remove oil, particularly the cooking oil used for frying and still have a good tasting food product. It is conventional wisdom in the food industry that in order to produce a reduced fat food product a process other than frying in cooking oil must be used.
There have been numerous processes proposed to produce snack food products having the palate appeal of fried food products, but being substantially fat-free. Unfortunately, none of these processes has met with a great deal of success. The typical commercial process attempts to produce a food product, such as potato chips without frying, but which they hope will have the flavor of fried products.
For example, U.S. Pat. No. 4,756,916 teaches a process for producing low-fat potato chips comprising washing potato slices with an aqueous solution, then applying oil to the washed slices to coat the slices with oil. The amount of oil applied to the washed slices is adjusted to achieve an oil content of about 10 to 25 wt. % in the final product. The oil coated slices are blanched, essentially pre-frying the slices due to the oil coating, then baked at a temperature of at least about 390.degree. F. to partially dry the slices. The partially dried potato slices are then baked at a temperature of about 290.degree. F. (140.degree. C.) to 320.degree. F. (160.degree. C.) to finish drying the slices.
Another technique is taught in U.S. Pat. No. 4,906,483 which is directed to a process for producing potato products having no-fat, no-cholesterol, and no salt ingredient characteristics. This is done by placing a pan, containing previously rinsed and sliced potatoes submerged in water, into a microwave oven until the submerged potatoes are visibly transparent. The hot water is then replaced with cold water to remove visible starch. The potatoes are rinsed and arranged on a non-stick cooking sheet and placed in a conventional oven for browning and crisping. Such a process fails to achieve the taste benefits that would be derived from frying the potatoes in cooking oil. Furthermore, extra steps are needed wherein a microwave and a conventional oven are used. Similarly, U.S. Pat. No. 5,202,139 discloses a process for preparing essentially fat-free potato chips. The process involves slicing and washing raw potatoes, pre-drying and arranging the sliced potatoes on a conveyor, then exposing them to a high intensity microwave field. The potato slices are then seasoned and exposed to a lower intensity microwave field. Such a process is not only limited by the fact that it does not achieve the taste advantage from frying, but the process itself is limited to producing only a single layer of product at a time. This limitation is due to the nature of microwave cooling and thus will result in less efficient chip production than a process that can cook or fry multiple layers of sliced food product.
Further, U.S. Pat. No. 4,919,965 discloses a method of toasting agricultural produce slices and, more particularly, potato slices. The toasting process takes place by the use of compressive, opposed, contact surfaces which toast the sliced produce in a fat and oil-free environment. More specifically, the process of this reference includes washing raw agricultural produce, then slicing the produce into thin slices. A seasoning is then applied to the slices which are then cooked under heat and pressure imposed between an opposing pair of heating surfaces to drive out moisture and toast the slices.
Also, U.S. Pat. No. 4,873,093 discloses a product and process for preparing a baked snack food from gelatinized starch ingredients wherein at least one ingredient having starch, such as potatoes, is mixed with water to form a composition which is steamed to form a dough-like consistency. The dough-like composition is then machined to form pieces which are baked in a conventional oven. The exterior layer of the dough-like composition cooks rapidly during baking and traps steam in the interior portion of the dough. An alternative embodiment includes spraying vegetable oil onto the pieces prior to baking to obtain a final product having a flat, oil-containing cracker-like appearance. A post-bake oil application is optional and included in a preferred embodiment.
U.S. Pat. No. 5,298,707 teaches a process and apparatus for preparing fat-free snack chips by exposing sliced raw potatoes, and the like, to a high intensity microwave field that rapidly converts moisture within the slice to steam. The exposed slices are then dried by longer exposure to a lower energy microwave field with an elaborate microwave apparatus. The resulting chip product, which has not been fried in oil will lack the flavor which appeals to the typical consumer of snack foods.
Another attempt at making fat-free snack foods is taught in U.S. Pat. No. 5,370,898 which discloses a process for producing food chip products which does not involve oil-based cooking. The process includes slicing and/or shaping a food, such as potatoes, then washing starch from the sliced, or shaped food, with water then forming multiple layers of the food product. The multiple-layered food product is baked in an impingement oven under conditions sufficient to form a fluidized bed of layered food product. The pressure is varied within the impingement oven to further release moisture. After baking, the shaped food forms are dried and optionally seasoned. This process, like those previously discussed, fails to produce a fried snack product substantially free of oil and which still has most, of not all, of the flavor generated by the frying step.
While conventional solvent extraction methods have met with various degrees of commercial success, they all require relatively high pressures and temperatures. Consequently, there remains a need in the art for an improved solvent extraction method which is more energy and cost efficient and which does not require elevated temperatures and pressures